That makes little intuitive sense to me. Help me understand why increasing the number of entities which possess a potential-weapon is beneficial for humanity?

If the US had developed a nuclear armament and no other country had would that truly have been worse? What if Russia had beat the world to it first? Maybe I'll get there on my own if I keep following this reasoning. However there is nothing clear cut about it, my strongest instincts are only heuristics I've absorbed from somewhere.

What we probably want with any sufficiently destructive potential-weapon are the most responsible actors to share their research while stimulating research in the field with a strong focus on safety and safeguarding. I see some evidence of that.